Valve stem packing is commonly used in process control valves. In the past, the criteria for selecting stem packing was simply to strike a balance between leakage and friction. Packing box leakage, although not desired, was not a significant concern for many process industries until valve consumers became cost conscious about material losses and recognized that valve stem packing leakage contributed to pollution. The EPA also recognized that stem packing leakage contributed to pollution and set standards for acceptable limits. Many of the largest consumers of process control valves also set their own standards for leakage and friction requirements.
This new interest in valve stem packing performance prompted the industry to develop low-friction packing systems that seal well and provide predictable performance. One development in stem packing is the use of different packing materials in combination, which provides resiliency along with high-pressure sealing capability, that remains consistent throughout the life of the valve packing. For example, Garlock Sealing Technologies markets an ultra-low emission valve stem packing product that uses a single ring of a first braided packing material that is soft and resilient interposed between four rings of a second braided packing material.
In order to realize the benefits of such technology, the correct types of packing material must be installed in the correct order and in the correct amounts. Typically, stem packing materials are provided on large spools and sold by the pound. Thus, consumers are left to determine how much of each type of packing material is required for their facility. Spools also may be difficult to store and may eventually come unraveled possibly resulting in damaged packing material or wasted packing material. Also, storing many different styles of packing material together may lead to confusion regarding which types of packing materials are to be used in combination. Furthermore, where the quantities of materials do not match in the ratio required, there may be a tendency to substitute one material for another leading to insufficient performance of the stem packing system.
Accordingly, there is a need for a stem packing dispenser that provides the correct ratio of materials for a given stem packing system. Furthermore, it is desirable that such a stem packing dispenser protects the packing from damage and provides a convenient means of transporting, storing, and reordering the product.